The embodiments disclosed herein generally relate to coated xerographic prints. The coated prints have toner-based image stability under conditions of high temperature, humidity and/or pressure.
In conventional xerography, electrostatic latent images are formed on a xerographic surface by uniformly charging a charge retentive surface, such as a photoreceptor. The charged area is then selectively dissipated in a pattern of activating radiation corresponding to the original image. The latent charge pattern remaining on the surface corresponds to the area not exposed by radiation. Next, the latent charge pattern is visualized by passing the photoreceptor past one or more developer housings comprising toner, which adheres to the charge pattern by electrostatic attraction. The developed image is then fixed to the imaging surface or is transferred to a receiving substrate, such as paper, to which it is fixed by a suitable fusing technique, resulting in a xerographic print or toner-based print.
Although xerographic equipment is used worldwide, it possesses a significant disadvantage in that in some cases the energy consumption is quite high. Thus, equipment with lower power consumption has been designed. Toners that function in the lower power consumption equipment, known as “low-melt toners,” are designed to have low glass transition temperatures (Tg's) of about 55° C. to about 65° C. However, an image defect known as document offset (or “blocking”) can occur at temperatures as low as about 54° C. to as high as about 70° C. or more, which is when the toner begins to melt. Thus, low-melt toners often have a significant document offset problem. The onset of document offset for various toners is set forth in Table 1.
TABLE 1Comparison of Onset Temperatures for DocumentOffset for Various Low-Melt TonersTonerMachineTemperature*FC IIDC2060 & DC1262° C.(144° F.)FC IDC40 & Majestik .RTM.61° C.(142° F.)(Xerox Corp.)5090DT18055.5° C.(132° F.)C6 & M4iGen3 .RTM. (Xerox Corp.)55.5° C.(132° F.)*where Document Offset (DO) = 4.0 @ 10 g/cm.sup.2
At document offset-provoking temperatures, when combined with pressure, such as several reams of paper in an output tray of a printer, some toner will stick to the sheet above it, or, in the case of duplex printing, the toner on the sheet above it. This yields two sheets that have to be pulled apart. In the worse case scenario, the toner pulls off part of the image on or paper fibers from the sheet above it. Clearly, this results in a loss of quality of the toner-based print (also referred to as a toner-based image, xerographic print, or xerographic image).
Known methods of reducing document offset include adding wax to the toner and applying an overprint coating to the substrate. The overprint coating, often referred to as an overprint varnish or composition, is typically a liquid film coating that may be dried and/or cured. Curing may be accomplished through drying or heating or by applying ultraviolet light or low voltage electron beams to polymerize (crosslink) the components of the overcoat. Overprint coatings are described in U.S. Pat. Nos. 4,070,262, 4,071,425, 4,072,592, 4,072,770, 4,133,909, 5,162,389, 5,800,884, 4,265,976, 5,219,641, and 7,166,406, and U.S. Patent Publication Nos. 2005/0250038, 2005/0250039 and 2007/0021522.
It would be useful to develop further systems and methods for treating xerographic prints to provide for stability under conditions of high heat and/or high humidity.